Titanium dioxide pigment composition

ABSTRACT

The invention relates to a titanium dioxide pigment mixture comprising a pigment having high greying stability (pigment type A) and a pigment having increased SiO 2  and Al 2 O 3  content in flaky precipitation (pigment type B). Said mixture provides, for example in paper, a high level of opacity for sufficient greying stability. If necessary, the light-fastness of the paper can be further increased by means of known production-conditioned measures on pigment type B.

The invention relates to a titanium dioxide pigment composition.

For certain applications, white papers are required to have high opacity(hiding power), high brightness with the most neutral possible tone, andgood greying resistance (light-fastness). Titanium dioxide pigments(laminating paper pigments) with a low tendency to greying are known.However, the amount of these pigments that can be incorporated intopapers is often limited because, in the event of an excessive pigmentconcentration, the physical properties of the paper no longer meet therequirements, e.g. for sufficient wet strength. Consequently, there arelimits to the opacity that can be achieved with the customary pigments.

It is known (U.S. Pat. No. 3,510,335) that the hiding power of titaniumdioxide pigments that are particularly suitable for the production of(matte) emulsion paints can be increased by means of a special type ofpost-treatment. They are coated to a relatively high level (at least 5%by weight) with silicon oxide and aluminium oxide, the coating beingapplied by a precipitation method aimed at achieving the mostvoluminous, porous, flocculent, loose, “fluffy” coating possible. Theirgreying resistance is, however, inadequate.

It has also been found that neither a “classical laminating paperpigment” with additional “emulsion paint pigment” post-treatment, nor an“emulsion paint pigment” with additional “laminating paper pigment”post-treatment is suitable for certain applications.

Consequently, it is expected of an improved laminating paper pigmentthat it be capable of achieving higher opacity, while retaining the samelevel of pigmentation and unchanged physical properties, especially wetstrength. It is, of course, also a desirable goal to be able to reducethe amount of pigment used to achieve a required degree of opacity whenusing an improved pigment.

Surprisingly, the above-mentioned object is solved not by a singlepigment, but by a titanium dioxide pigment blend consisting of the twopigment types, laminating paper pigment and emulsion paint pigment. Ithas been found that the addition of a pigment with a high level ofspecial post-treatment, a kind of “booster pigment”, to a classicallaminating paper pigment results in a pigment blend that achieves thedesired improvement in opacity described above, while also offeringsufficient greying resistance, brightness and wet strength.

The invention relates to a blend of a pigment with high greyingresistance, a typical laminating paper pigment (Pigment Type A), and aspecial emulsion paint pigment (Pigment Type B) characterised by anelevated SiO₂ and Al₂O₃ content applied by precipitation in flocculentform.

It achieves improved values as regards opacity, together with sufficientgreying resistance, brightness and wet strength. The increase in opacitywhen using an unchanged quantity of TiO₂, or the possibility ofachieving unchanged opacity with a lower level of TiO₂ input, gives riseto both technical and economic advantages.

Further advantageous embodiments are described in the sub-claims. Anexample of the invention is described in further detail below.

The pigments open to consideration as Pigment Type A includepost-treated titanium dioxide pigments, whose base material can bemanufactured by the sulphate process (SP) or the chloride process (CP),and which preferably have a rutile structure. The base material need notbe stabilised, although special stabilisation is preferred: for CP basematerial, by Al doping of 0.3 to 3.0% by weight (calculated as Al₂O₃)and an oxygen surplus of at least 2% in the gas phase during oxidationof the titanium tetrachloride into titanium dioxide; for SP basematerial, by doping with, for example, Al, Sb, Nb or Zn (“light”stabilisation with Al is preferred for achieving sufficiently highbrightness, or compensation with antimony in the case of largerquantities of Al dopant).

The pigments are typically given inorganic post-treatment with Al, Pand/or Si compounds. Additional post-treatment with cerium and/ornitrate and/or zinc compounds serves to improve the greying resistanceof the laminates, as does tempering at temperatures between 200 and 700°C., preferably 400 to 600° C.

Pigment Type A can also be characterised by its light-fastness value,assessed in the laminate: the grade on the blue wool scale (ISO 4586-2)is greater than 6; the CIELAB ΔL* greying value (DIN 6174) is less than1.5 after 96 hours of exposure in the Xenotest.

Pigments with high greying resistance (Pigment Type A) are, for example,commercially available under the designation KRONOS® 2080, 2081, 2084and 2087.

The pigments open to consideration as Pigment Type B includepost-treated titanium dioxide pigments, whose base material can bemanufactured by the sulphate process or the chloride process, and whichpreferably have a rutile structure. The base material is preferably alsostabilised: for CP base material, by Al doping of 0.3 to 3.0% by weight(calculated as Al₂O₃) and an oxygen surplus of 2 to 15% during gas phaseoxidation of the TiCl₄ into TiO₂; for SP base material, by doping with,for example, Al, Sb, Nb or Zn (“light” stabilisation with Al ispreferred for achieving sufficiently high brightness, or compensationwith antimony in the case of larger quantities of Al dopant).

The pigments have a relatively high level of inorganic post-treatmentwith Al and Si compounds; the Al content (calculated as Al₂O₃) is atleast 2% by weight and the Si content (calculated as SiO₂) at least 3%by weight, where the sum of the Si and Al components (calculated asoxide) totals at least 7% by weight.

According to the invention, one special characteristic of Pigment Type Bis the flocculent, loose structure of the inorganic post-treatment skinon the base material. The aim is to achieve the most voluminous, porous,flocculent, loose, “fluffy” coating possible (described in U.S. Pat. No.3,510,335, for example)—the opposite to “dense-skin treatment”, as itwere (described in U.S. Pat. No. 2,885,366). In dense-skin treatment,the post-treatment skin is supposed to enclose the TiO₂ particles ascompletely as possible, in order to reduce the undesirablephotocatalytic effect of the TiO₂ pigment on the surrounding matrix. Incontrast, the flocculent nature of the oxide or oxyhydrate layer ofPigment Type B results in improved dispersion of the pigment in a matrixand makes a decisive contribution to increasing the opacity. The looselyprecipitated, inorganic oxide or oxyhydrate layer on the TiO₂ core actsas a spacer between the scattering particles.

Pigment Type B can also be characterised by property values. Parametersinfluenced by the “unevenness” or the compactness of the post-treatmentskin are suitable for this purpose. A measure of the unevenness is, forexample, the oil absorption or the specific surface area; a measure ofincomplete coverage is, for example, the H₂SO₄ solubility of the pigment(the pigment is dispersed in concentrated sulphuric acid and thesuspension kept at 175° C. for one hour; the soluble TiO₂ is determinedin the filtrate after filtration): Pigment Type B according to theinvention has elevated oil absorption (at least 25) or relatively highH₂SO₄ solubility (at least 15% TiO₂ dissolved).

The pigment blend according to the invention can also be characterisedby property values assessed in the laminate. The following values referto papers with an ash content of 40±1% and a grammage of 100±1 g/m².

-   a) Opacity    -   i) CIELAB L*_(black)≧90.0    -   ii) Opacity value L≧90.7-   b) Light-fastness    -   i) Blue wool scale: Grade>6    -   ii) CIELAB ΔL*<2.0        Using a pigment blend according to the invention, the wet        maximum load achieved for a paper (produced on the laboratory        sheet former) is at least 3.7 N.

All the requirements imposed in the laminate sector are met by thepigment blend according to the invention.

The following measures, in particular, permit further advantageousimprovements for Pigment Type B, especially in relation to the laminategreying resistance:

-   a) Supplementary additions of cerium, zinc or nitrate compounds    during post-treatment or, in the case of nitrate, particularly    preferably to the filter paste prior to drying. The addition of    nitrate compounds during the final milling of the pigment is    likewise possible.-   b) Prior to the post-treatment that leads to the loose, “fluffy”    post-treatment skin of SiO₂ and Al₂O₃ in the sense of this    invention, an initial post-treatment step corresponding to that of    Pigment Type A.

EXAMPLES OF PIGMENT TYPES A AND B (TABLE 1)

Pigment A1

Rutile pigment produced by the CP method and post-treated with 5.5 to7.5% by weight* of an aluminium compound (calculated as Al₂O₃), 1.0 to3.0% by weight of a phosphorus compound (calculated as P₂O₅) andadditionally with 0.18 to 0.24% by weight of a nitrate; the propertyvalues are summarised in Table 1. A similar, typical “laminating paperpigment” is, for example, commercially available under the name KRONOS®2080.

* All percent-by-weight data for post-treatment substances in theexamples refer to the base material used.

Pigment B1

Pigment based on base material with a rutile structure, produced by theSP method without special stabilisation. The pigment has a relativelyhigh level of inorganic post-treatment, where flocculent precipitationof the oxide layer is achieved by an appropriate process (production ofa milled slurry at a pH value of 10.5; addition of 2.5% by weight H₂SO₄and 5.1% by weight SiO₂ in the form of sodium silicate solution over 30minutes; further pH reduction after a retention time of 30 minutes with2.5% by weight H₂SO₄; addition of 5.1% by weight SiO₂ in the form ofsodium silicate solution; after stirring for 30 minutes, addition of2.3% by weight Al₂O₃ in the form of aluminium sulphate solution over 45minutes, followed by stirring for 90 minutes; renewed addition of 2.9%by weight Al₂O₃ in the form of sodium aluminate solution, followed bywashing and drying after a retention time of 60 minutes). The propertyvalues are given in Table 1.

Pigment B2

Pigment based on milled base material with a rutile structure withoutspecial stabilisation, as in Pigment B1. Flocculent precipitation byaddition of 3.2% by weight H₂SO₄ over 30 minutes, followed by 3.2% byweight SiO₂ in the form of sodium silicate solution over 30 minutes;3.5% by weight Al₂O₃ is subsequently added in the form of sodiumaluminate solution, followed by stirring for 30 minutes; 2.0% by weightAl₂O₃ is then added in the form of aluminium sulphate solution and thesuspension is filtered after a retention time of 60 minutes. Furthertreatment is carried out as for Pigment B1. In terms of “fluffiness”, B2is at the lower limit of Pigment Type B.

Pigment B3

Pigment based on SP base material stabilised with 0.01% by weight Al(calculated as Al₂O₃). Post-treatment over 15 minutes with 1.0% byweight P₂O₅ in the form of disodium hydrogenphosphate solution, over 10minutes with 1.6% by weight Al₂O₃ in the form of aluminium sulphatesolution and over 4 minutes with 1.4% by weight Al₂O₃ in the form ofsodium aluminate solution. After adjusting the pH value to 4 with H₂SO₄over 30 minutes, addition of 3.0% by weight SiO₂ in the form of sodiumsilicate solution together with aluminium sulphate solution (100 gAl₂O₃) in such a quantity that the pH value of 4 remains constant,followed by addition of 4.7% by weight Al₂O₃ in the form of sodiumaluminate solution over 12 minutes and thereafter again of 2.2% byweight Al₂O₃ in the form of aluminium sulphate solution over 15 minutes.See Table 1 for the property values.

Pigment B4

Pigment based on SP base material stabilised with 0.6% by weight Al(calculated as Al₂O₃). It is milled and post-treated as described underB1 and, following the addition of 0.4% by weight nitrate to the filterpaste in the form of sodium nitrate, dried and milled. See Table 1 forthe property values.

Pigment B5

Pigment based on SP base material stabilised with 0.6% by weight Al(calculated as Al₂O₃). After milling, it is slurried and the pH valuelowered with 1.9% by weight H₂SO₄; addition of 3.8% by weight SiO₂ inthe form of sodium silicate solution over 20 minutes; after a retentiontime of 10 minutes, addition of 1.9% H₂SO₄ to lower the pH value;renewed addition of 3.8% by weight SiO₂ in the form of sodium silicate;after stirring for 10 minutes, addition of 2.0% by weight Al₂O₃ in theform of aluminium sulphate solution over 10 minutes, followed byaddition of 3.2% by weight Al₂O₃ in the form of sodium aluminate; aftera retention time of 60 minutes, filtration, washing, drying, milling.

Pigment B6

Pigment based on SP base material stabilised with 0.6% by weight Al(calculated as Al₂O₃). Following wet-milling, it is slurried and the pHvalue lowered with 2.9% by weight H₂SO₄; addition of 6.0% by weight SiO₂in the form of sodium silicate solution over 30 minutes; 10 minutes'retention time; addition of 0.7% by weight Al₂O₃ in the form ofaluminium sulphate solution over 5 minutes, followed by 3.7% by weightAl₂O₃ in the form of sodium aluminate solution and subsequently afurther 1.1% by weight Al₂O₃ in the form of aluminium sulphate solution,stirring for 10 minutes between each addition. Further processing as forB5.

Pigment B7

This pigment differs from Pigment B6 only as regards the amount of thepost-treatment substances. The quantities are as follows:

-   -   4.7% H₂SO₄    -   9.0% SiO₂ in the form of sodium silicate over 45 minutes    -   0.7% Al₂O₃ in the form of aluminium sulphate    -   3.8% Al₂O₃ in the form of sodium aluminate    -   0.9% Al₂O₃ in the form of aluminium sulphate        All other process steps are comparable.

Typical values are compiled in Table 1. Compared to a standardlaminating paper pigment (Pigment Type A), the oil absorption, H₂SO₄solubility and BET surface are higher.

While Pigments B1 to B7 achieve the required values for opacity,expressed here by the values CIELAB L*_(black) and opacity value L, thegreying resistance in the laminate and, in the case of Pigment B2, alsothe wet strength in the paper are inadequate.

Assessment of the Pigments and Pigment Blends in Laminates

a) Laminate Production (Laboratory Scale)

A 36.5% aqueous pigment suspension made of 146 g titanium dioxidepigment (or pigment blend) and 254 g tap water is prepared. Testing isbased on 30 g pulp (oven-dry). The corresponding quantity of pigmentsuspension is adapted to the retention and the required ash content,40±1% in this case, or the grammage, 100±1 g/m² in this case. A personskilled in the art is familiar with the procedure and the auxiliariesused. The sheet to be impregnated with resin is immersed in a resinsolution and pre-condensed for 25 seconds at 130° C. in arecirculating-air drying oven. Impregnation is performed a second timein similar manner. The resin solution amounts to 129 to 140% of thegrammage. The sheet has a residual moisture content of 4 to 6% byweight. The condensed sheets are combined into stacks with phenolicresin-impregnated core papers, and white and black underlay paper. Thelaminate structure used for the test comprised 9 layers: paper, paper,core paper, core paper, underlay consisting of black underlay, corepaper, core paper, black/white underlay, paper. The stacks are pressedfor 300 seconds with the help of a Wickert® Type 2742 laminating pressat a temperature of 140° C. and a pressure of 90 bar.

b) Opacity

The opacity is a measure of the light transmission of the paper. Thefollowing are selected as a measure of the opacity of the laminates:

-   i) CIELAB L*_(black), the brightness of the laminates measured over    black underlay paper.-   ii) Opacity value L [%]=Y_(black)/Y_(white)×100, determined from the    Y-value measured over black underlay paper (Y_(black)) and the    Y-value measured over white underlay paper (Y_(white)).    The values are measured using a spectrophotometer (ELREPHO 3300).

c) Light-Fastness

To assess the greying resistance (light-fastness) of the titaniumdioxide pigments or pigment blends, the corresponding laminate samplesare exposed in a XENOTEST 150S. The side of the laminate on which twopapers are laminated together is measured for the assessment.

-   i) Greying, CIELAB ΔL*    -   The CIELAB L* brightness to DIN 6174 is measured before and        after 96 hours of exposure in the Xenotest. The light source is        a xenon-arc lamp. The temperature inside the device is 23±3° C.,        the relative humidity being 65±5%. The samples are rotated        during the exposure cycle.-   ii) Blue wool scale    -   The light-fastness is assessed on the basis of ISO 4586-2 (1995)        with the help of the “blue wool scale”.

d) Wet Maximum Load

To assess the wet strength of the papers, they are initially stored(“matured”) at 105° C. for 24 hours. Test strips of 15 mm width aresoaked in distilled water for 5 minutes. The wet maximum load of the wetstrips is subsequently tested with the help of tensile test apparatus.The wet strength is stated in Newton.

e) Determination of Optical Values

The optical values (CIELAB L*, a*, b*) are determined to DIN 6174 withthe help of the ELREPHO® 3300 spectrophotometer. The side of thelaminate on which two papers were laminated together is measured for theassessment.

Characteristic Performance Values for Individual Pigments and PigmentBlends (Table 2)

Test 1 (Standard Laminating Paper Pigment), Pigment A1 Only

Pigment A1, comparable to KRONOS® 2080, is used in pure form. Thelaminates are produced in accordance with the test method describedabove. Papers with an ash content of 40% and a grammage of 100 g/m² areproduced in each case. To set the ash content, the necessary quantity ofTiO₂ suspension is added to the pulp in each test. The targeted grammageof 100 g/m² is set via the quantity of pigment/pulp suspension. Thequantities of TiO₂ suspension used in each case, and the quantity ofpigment/pulp suspension, are listed in Table 2.

Test 2 (Standard Emulsion Paint Pigment), Pigment B1 Only

Test Pigment B1, which corresponds to a standard emulsion paint pigment,is used in pure form. The results of Test 2 are given in Table 2.Pigment B1 displays excellent opacity in comparison with A1. However,its greying resistance is low and unacceptable. Moreover, the sheetsdisplayed very poor wet strength, i.e. they were very soft and toreeasily during impregnation.

Test 3 (Standard Emulsion Paint Pigment), Pigment B2 Only

Pigment B2 is a standard emulsion paint pigment with a lower level ofsurface treatment compared to Pigment B1. The pigment is used in pureform. The results of Test 3 are listed in Table 2. Laminates containingPigment B2 display significantly higher opacity compared to Pigment A1as the reference standard, but are less good in comparison with PigmentB1. Pigment B2 likewise demonstrates inadequate greying resistance.There are no disadvantages in terms of wet strength.

Test 4 (A1/B2 Blend)

A pigment blend consisting of 70% by weight Pigment A1 and 30% by weightPigment B2 is used in this test. The results of Test 4 are listed inTable 2. This laminate containing a 70:30 pigment blend displaysimproved opacity compared to Test 1. The greying resistance is stillacceptable.

Test 5 (A1/B3 Blend)

A pigment blend consisting of 70% by weight A1 and 30% by weight B3 isused in this test. The latter is based on a bright, lightly stabilisedbase material with “classical laminating paper pigment post-treatment”and additional “emulsion paint pigment post-treatment”. The results ofTest 5 are listed in Table 2. The above pigment blend results inlaminates with substantially better opacity compared to Test 1, thegreying resistance being at an acceptable level.

Test 6 (A1/B4 Blend)

A pigment blend consisting of 70% by weight Pigment A1 and 30% by weightPigment B4 is used in this test. Pigment B4 has similar surfacetreatment to Pigment B1, but is produced using highly stabilised basematerial. The results are listed in Table 2. It can be seen that theswitch to highly stabilised base material greatly improves the greyingresistance. The laminates display substantially improved opacitycompared to Test 1. The wet strength of the papers is lower than withpure A1, but acceptable.

Test 7 (A1/B5 Blend)

A pigment blend consisting of 70% by weight Pigment A1 and 30% by weightPigment B5 is used in this test. The latter is a pigment with surfacetreatment similar to that of Pigment B4, but produced with approx. 25%less SiO₂ surface treatment. The results of Test 7 are listed in Table2. Owing to the lower level of SiO₂ surface treatment of B5 compared toB4, this blend displays poorer opacity in comparison with Test 6, butcomparable greying resistance.

Test 8 (A1/B6 Blend)

A pigment blend consisting of 70% by weight Pigment A1 and 30% by weightPigment B6 is used in this test. Pigment B6 has surface treatmentsimilar to that of Pigment B2, but with twice the quantity of SiO₂. Thesame highly stabilised base material is used as for B4. The results ofTest 8 are listed in Table 2. The opacity of the laminate sampleproduced using this pigment blend is substantially higher than thatobtained with pure A1. The wet strength is adequate and the greyingresistance good.

Test 9 (A1/B7 Blend)

A pigment blend consisting of 70% by weight Pigment A1 and 30% by weightPigment B7 is used in this test. The latter pigment has surfacetreatment similar to that of Pigment B6. The. results of Test 9 arelisted in Table 2. Owing to a higher quantity of SiO₂ compared to Test8, this pigment blend leads to a laminate with very high opacity values,substantially higher than obtained with pure Pigment A1. The greyingresistance is at a good level. The wet strength of the papers containingthe above pigment blend is tolerable at the upper limit.

Titanium dioxide pigment compositions are preferred in which the contentof Pigment Type B is between 10 and 90% by weight, particularlypreferably 30 to 50% by weight, of the pigment blend.

TABLE 1 Pigment A1 B1 B2 B3 B4 B5 B6 B7 Al₂O₃ post-treatment quantity6.5 5.2 5.5 10.2 5.2 5.2 5.5 5.4 (% referred to base material) SiO₂post-treatment quantity <0.01 10.2 3.2 3.0 10.2 7.6 6.0 9.0 (% referredto base material) Oil absorption (g/100 g) 18 40 26 29 41 49 35 34 H₂SO₄solubility 15 19 16 23 19 19 18 19 (% TiO₂ dissolved) BET surface (m²/g)9 49 29 34 45 45 40 53

TABLE 2 Test 1 2 3 4 5 6 7 8 9 Pigment blend A1: 100 — — A1: 70 A1: 70A1: 70 A1: 70 A1: 70 A1: 70 (in %) — B1: 100 B2: 100 B2: 30 B3: 30 B4:30 B5: 30 B6: 30 B7: 30 TiO₂ suspension used [g] 120 120 100 115 105 10599 106 112 Pigment/pulp suspension [g] 425 430 435 423 440 425 430 420423 Opacity (laminate) CIELAB L*_(black) 90.0 91.4 90.8 90.2 90.4 90.690.5 90.5 90.9 Opacity value L 90.7 94.3 93.4 91.5 91.9 92.5 92.9 9292.8 Greying (laminate) ΔL* 0.9 4.5 6.9 2.0 1.5 1.2 1.3 1.3 1.3 Bluewool scale [grade] >6.0 <6.0 <6.0 >6.0 >6.0 >6.0 >6.0 >6.0 >6.0 Wetmaximum load [N] 5.5 2.3 4.1 4.6 4.4 4.1 3.8 4.8 3.7 Optical values(laminate) CIELAB L*_(white) 93.4 93.8 93.3 93.3 93.4 93.4 93.3 93.293.7 CIELAB a*_(white) −1.4 −1.3 −1.4 −1.4 −1.3 −1.3 −1.4 −1.4 −1.3CIELAB b*_(white) 2.2 2.8 3.2 2.6 2.5 2.6 2.8 2.7 2.6

1. A titanium dioxide pigment blend composition comprising; a PigmentType A having a first titanium dioxide base material, the Pigment Type Ahaving high greying resistance, wherein the high greying resistance isdefined by a grade on the blue wool scale (ISO 4586-2) of greater than6; and a Pigment Type B with an increased Si and Al content applied byprecipitation of Si and Al compounds in flocculent form on to a secondtitanium dioxide base material, wherein the weight of the increased Sicontent of the Pigment Type B (calculated as SiO₂) is at least 3% of theweight of the titanium in the second titanium dioxide base pigmentmaterial and the total of the Si and Al weights (calculated as SiO₂ andAl₂O₃) is at least 7% of the weight of the titanium in the secondtitanium dioxide base pigment material.
 2. The titanium dioxide pigmentblend composition according to claim 1, characterized in that the secondtitanium base material is manufactured by the sulphate process,stabilised with up to 1% by weight aluminium (calculated as Al₂O₃). 3.The titanium dioxide pigment blend composition according to claim 1,characterized in that the second titanium dioxide base material ismanufactured by the chloride process, stabilised with up to 3% by weightaluminium (calculated as Al₂O₃).
 4. The titanium dioxide pigment blendcomposition according to claim 1, characterized in that the secondtitanium dioxide base material is coated immediately, initially withaluminium phosphate.
 5. The titanium dioxide pigment blend compositionaccording to claim 1, characterized in that the titanium dioxide basematerial is additionally coated with up to 0.2% by weight cerium(calculated as CeO₂) and/or up to 2.5% by weight zinc (calculated asZnO).
 6. The titanium dioxide pigment blend composition according toclaim 1, characterized in that the Pigment Type B displays a nitratecontent of up to 1% by weight (referred to the second titanium dioxidebase material) and/or tempering at up to 500° C.
 7. The titanium dioxidepigment blend composition according to claim 1, characterized in thatthe weight of Pigment Type B relative to the weight of the pigment blendis between 10 and 90%, preferably 30 to 50%.
 8. The titanium dioxidepigment blend composition of claim 4, wherein second titanium dioxidebase material is additionally coated with up to 0.2% by weight cerium(calculated as CeO₂) and/or up to 2.5% by weight zinc (calculated asZnO).
 9. The titanium dioxide pigment blend composition of claim 4,wherein the Pigment Type B displays a nitrate content of up to 1% of theweight of the titanium in the second titanium dioxide base pigmentmaterial and/or tempering at up to 500° C.
 10. The titanium dioxidepigment blend composition of claim 4, wherein the weight of Pigment TypeB relative to the pigment blend is between 10 and 90%, preferably 30 to50%.
 11. The titanium dioxide pigment blend composition of claim 5,wherein the Pigment Type B displays a nitrate content of up to 1% of theweight of the titanium in the second titanium dioxide base pigmentmaterial and/or tempering at up to 500° C.
 12. The titanium dioxidepigment blend composition of claim 5, wherein the weight of Pigment TypeB relative to the weight of the pigment blend is between 10 and 90%,preferably 30 to 50%.
 13. The titanium dioxide pigment blend compositionof claim 6, wherein the weight of Pigment Type B relative to the weightof the pigment blend is between 10 and 90%, preferably 30 to 50%.